Lateral Gene Transfer in Dental Plaque
Lateral gene transfer, also known as horizontal gene transfer, refers to the transfer of genetic material in a manner other than reproduction. Three major forms of lateral gene transfer in prokaryotes are a) conjugation: self-transmissible DNA (e.g. F plasmid) transfer via F pilus formed between cell-cell contact; b) transformation: uptake of free extracellular DNA by naturally competent cells; and c) transduction: DNA is introduced by the infection of bacteriophages to the host bacteria. Lateral gene transfer gives the recipient cells novel genes, thus helps bacterial to better adapt to the environment, to compete with other organisms, and to promote their survival, virulence and pathogenicity. Biofilm is a community of single or multiple microorganism species attaching to a surface and surrounded by a layer of extracellular polymeric substance. Dental plaque is a multispecies biofilm growing on the surface of teeth. The large population of microbe cells and close proximity between cell and cell make the dental plaque an ideal place for lateral gene transfer to happen. In the following are a couple of examples of lateral gene transfer in different species in dental plaque. Lateral gene transfer in Porphyromonas gingivalis '' ''Porphyromonas gingivalis is a gram-negative anaerobic bacterial pathogen in dental plaque. In P. gingivalis, the major form of lateral gene transfer is transformation via natural competence, whereas conjugation has a minor role. Extracellular DNA (eDNA) is a component of the extracellular polymeric substrate in biofilm, so the abundance of eDNA allows the natural transformation to happen frequently in dental plaque. The expression of comF, a gene controlling the competence of P. gingivalis, is upregulated twofold in biofilm-cultured P. gingivalis ''than planktonic counterpart. Lateral gene transfer is important for the survival and pathogenicity of ''P. gingivalis in the periodontal pocket. Lateral gene transfer in Fusobacterium nucleatum Fusobacterium nucleatum is another Gram-negative opportunistic pathogen in periodontitis. Conjugation is the major form of lateral gene transfer in F. nucleatum. Fusobacterial plasmid pFN1 encodes relaxase gene that is involved in plasmid mobilization. The transfer of tetracycline resistance gene tetM is transferred between strains of F. nucleatum and from F. nucleatum to other bacteria such as Enterococcus faecalis and P. anaerobius. Interference of Lateral gene transfer Besides cooperation, there is also competition existing between different microbes in dental plaques due to the limited nutrients. Wang et al. demonstrated that Porphyromonas gingivalis and Treponema deticola ''are able to antagonize the natural transformation of ''Streptococcus mutans, thus blocking a major pathway of lateral gene transfer of S. mutans ''and may render ''S. mutans less virulent and more susceptible to environment antimicrobial factors. Therefore, lateral gene transfer can also be utilized as a promising target for antimicrobial and antibiotic design and drug development. Reference 1. Wang et al. Periodontal pathogens interfere with quorum-sensing-dependent virulence properties in Streptococcus mutans . J Periodontal Res. 2011 Feb;46(1):105-10 2. Signat B, et al. (2011). "Fusobacteriumnucleatum in Periodontal Health and Disease". Curr Iss Mol Biol 13 (2): 25–36. 3. Lo AW et al. Comparative transcriptomic analysis of Porphyromonas gingivalis biofilm and planktonic cells. BMC Microbiol 2009; 9: 18. 4. Olsen, I., Tribble, G. D., Fiehn, N.-E. & Wang, B.-Y. Bacterial sex in dental plaque. J. Oral Microbiol. 5, 1–9 (2013).